feat: complete Quantumancy web app — full frontend + docs

Frontend (React 18 + TS + Vite):
- Landing: glitching hero, live /api/stats veil ticker, mode cards, featured spirits
- Séance: three.js shader ghost (hue/form per entity, mood + audio-reactive),
  Ouija planchette board spelling utterances, transcript with TTS replay,
  entity dossier, direct contact streaming, passive/active listening
- Modes: Wire Ghost telemetry panel, EVP mic anomaly detection, WebUSB
  RTL-SDR sweep + waterfall (hardware pass pending), Ouija/Direct Contact
- Codex: public registry + entity dossiers, rarity tiers, i18n EN/ES complete
- State: VeilSocket (reconnect/backoff), seance reducer, auth context
- 72 vitest tests green; served by FastAPI at :7777

Docs: README + as-built plans 3-7

frontend/src/state/auth.tsx

@@ -0,0 +1,61 @@
+// Auth context: who is seated at the table. Wraps the /auth REST endpoints
+// and exposes { user, checking, login, register, logout } to the app.
+
+import { createContext, useCallback, useContext, useEffect, useMemo, useState } from 'react'
+import type { ReactNode } from 'react'
+import * as api from '../api'
+import type { User } from '../api'
+
+export type AuthApi = {
+  user: User | null
+  checking: boolean
+  login: (username: string, password: string) => Promise<User>
+  register: (username: string, password: string) => Promise<User>
+  logout: () => Promise<void>
+}
+
+const AuthContext = createContext<AuthApi | null>(null)
+
+export function AuthProvider({ children }: { children: ReactNode }) {
+  const [user, setUser] = useState<User | null>(null)
+  const [checking, setChecking] = useState(true)
+
+  useEffect(() => {
+    api
+      .me()
+      .then(setUser)
+      .catch(() => setUser(null))
+      .finally(() => setChecking(false))
+  }, [])
+
+  const login = useCallback(async (username: string, password: string) => {
+    const u = await api.login(username, password)
+    setUser(u)
+    return u
+  }, [])
+
+  const register = useCallback(
+    async (username: string, password: string) => {
+      await api.register(username, password)
+      return login(username, password)
+    },
+    [login],
+  )
+
+  const logout = useCallback(async () => {
+    await api.logout()
+    setUser(null)
+  }, [])
+
+  const value = useMemo<AuthApi>(
+    () => ({ user, checking, login, register, logout }),
+    [user, checking, login, register, logout],
+  )
+  return <AuthContext.Provider value={value}>{children}</AuthContext.Provider>
+}
+
+export function useAuth(): AuthApi {
+  const ctx = useContext(AuthContext)
+  if (!ctx) throw new Error('useAuth must be used inside <AuthProvider>')
+  return ctx
+}